The proposed research concerns the physiology of photoreceptors in vertebrate retinae. Individual, solitary photoreceptors will be dissociated from salamander and rabbit retinae. Salamander rods and a patch-pipette voltage clamp will be used to study the control of exocytosis by calcium, the voltage dependence of the sodium-potassium pump, and the electric properties of sodium-dependent carriers involved in synaptic transmitter release. Salamander cones and a single-micropipette voltage clamp will be used to study the effect of synaptic transmitters that interact with cones. Rabbit rods and a patch-pipette voltage clamp will be used to characterize the voltage-dependent currents of a mammalian photoreceptor. In addition, the layer of photoreceptors in rabbit retinae will be isolated by killing non-photoreceptor cells with toxins. The isolated layer of cells will be cultured and used to determine the identity of synaptic transmitters and their mechanism of release. Knowledge of the conditions necessary for culturing photoreceptors may reveal factors necessary for their normal development and survival following injury. Understanding the cellular and molecular mechanisms of neurotransmission may promote the development of drug therapies for retinal disorders. Investigating the mechanism for maintaining ion gradients may allow an understanding of conditions that promote the rescue of damaged photoreceptors.